As disclosed in Patent Literature 1, one induction-heated roller apparatus directly measures temperature with a temperature detecting element attached to a roll main body as a heated body.
Meanwhile, a roll main body is a rotating body, and therefore in many cases, it is not easy to attach a temperature detecting element. Also, in the case of attaching a temperature detecting element to a roll main body, a contact state between the temperature detecting element and the roll main body differs individually, which may cause an error in detected temperature. Further, in order to input an output from a temperature detecting element provided in a roll main body to a fixed control device, a sophisticated device such as a rotary transformer is required.
Also, it is possible to use non-contact type temperature detecting means such as a radiation pyrometer to detect the temperature of a roll main body; however, in such a case, it is often difficult to detect an accurate temperature because detection accuracy is low or the temperature is affected by a surface radiation rate (emission rate) of the roll main body.